We love Kishu! Also Cara Cara Oranges are great.
I have about 6 different budwood I’ve ordered from the CCCPP to graft onto an older Tangelo tree so I will let you know how that goes next year or after that 
… all of those are supposed to be excellent but no personal experience:
Cocktail Pummelo
Oroblanco Grapefruit
Wekiwa Tangelo
US Superna (USDA 88-2) Mandarin
Parent Washington Navel
Edit: I also have a small Dekpon tree that I originally bought as a budwood source for spring grafting but that I’ve been considering keeping as a tree by itself as well. We will see. I have very limited space so not sure if I have space for this. Can try in a pot maybe.
Also - we have a Pixie Mandarin and we like that too though I’ve heard some folks don’t like it as much for some reason. Apparently it can get too sweet! So you might have to do some research.
We also grafted Yuzu Lemon onto our Meyer Lemon and hoping for some Yuzu fruit this year or next.
Bearss Lime is great as well.
We also have a small Owari Satsuma Mandarin but that tree has stalled for the last 2 years at about 1.5ft so I’m about to transfer it to a pot and inspect the roots to see what’s up. It’s supposed to be great. Might also just use it as grafting material for either the Pixie Mandarin or the large Tangelo.
Hope this helps!